The Indian government has moved to stamp out protests that have swelled in New Delhi since the gang-rape of a young woman, banning gatherings of more than five people, but still thousands poured into the heart of the capital to vent their anger.

Police used tear gas and batons to hold crowds back from marching on the president's palace, just as they did the day before. About 30 to 35 people, including a few policemen, were being treated at a nearby hospital for injuries, two doctors said.

The 23-year-old victim of the December 16 attack, who was beaten, raped for almost an hour and thrown out of a moving bus in New Delhi, was still in a critical condition on respiratory support but responding to treatment, doctors said.

Six men have been arrested for the assault.

New Delhi has the highest number of sex crimes among India's major cities, with a rape reported on average every 18 hours, according to police figures.

Most sexual assaults go unreported and unremarked, but the brutality of last week's attack triggered the biggest protests in the capital since mid-2011 demonstrations against corruption that rocked the government of Prime Minister Manmohan Singh.

The protesters, predominantly students but also housewives and even children, are demanding more steps from the authorities to ensure safety for women - particularly better policing - and some want the death penalty for the accused.

Several metro stations were closed and many roads into the administrative centre of the city were barricaded on Sunday to prevent a build-up of protesters.

However, by late afternoon the crowd around the India Gate monument - normally a festive place on a Sunday - had swollen to several thousand.

Scuffles broke out near government buildings, where youths shouted "Down with Delhi police!" and threw bottles at the forces holding them back. Angry protesters later overturned a vehicle and seized police vans.